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Highlights • Water for energy sector in China's two biggest megalopolises was analyzed. • Energy sector in Jing-Jin-Ji had 2.41 km3 of water withdrawal footprint in 2010. • Energy sector in Yangtze Delta had 9.59 km3 of water withdrawal footprint in 2010. • Water consumption footprint was 848.06 and 973.91million m3 respectively. • Jing-Jin-Ji had much larger external water footprint than Yangtze Delta. Abstract Using a consumption-based Multi-Regional Input-Output (MRIO) model, we investigate the distinctive characteristics, self-efficiency or external dependency, of energy demand's water footprint in China's two biggest and fastest developing megalopolises. We find that energy demand water footprint in the Jing-Jin-Ji and the Yangtze Delta amounted to 2.41 and 9.59 billion m³of water withdrawal respectively in 2010, of which 848.06 and 973.91 million m³was consumed. Among all energy products, electricity contributed the largest share to the energy sector's water footprint in both regions. The sectoral distribution of water footprint in the upstream supply chain differed by region. Most significantly, the agricultural sector accounted for more than 30% of water consumption footprint. In addition to water used locally, final energy demands in these two regions induced external water footprint beyond their administrative boundaries. The Jing-Jin-Ji region's energy sector had a smaller water footprint compared to the water-abundant Yangtze Delta region. However, external water footprint occupied a larger proportion in the former. Such divergence can be attributed to the distinctive water endowments and water-using technologies utilized in their respective energy sectors. Bespoke urban governance and policies tailored to local resource and technology portfolios are recommended for different urban agglomeration energy and water flows. [ABSTRACT FROM AUTHOR]

The development of metropolitan cities inevitably relies on natural resources beyond their boundary through trade of materials and products, particularly within the same urban agglomeration. Meanwhile trade facilitates the optimization of resource allocations under scarcity, among cities and sectors, and therefore generates economic gains. This study constructs an economic evaluation model combining a Multi-Regional Input-Output model and a Data Envelopment Analysis (DEA) to quantify the economic impacts of virtual water trades among the 13 cities in the JingJinJi region (China national capital area), one of the most water-scarce regions in China. We found that the total virtual water trade among the 13 cities amounted to 927 million m3 in 2012, among which agricultural sectors contributed 90% while the industrial sector and service sector together made up the remaining 10%. While Beijing and Tianjin are the main virtual water importers, importing respectively 300.48 and 226.92 million m3 in 2012, Shijiazhuang was the largest virtual water exporter, exporting 173.29 million m3 virtual water in the same year. Due to their more advanced economic conditions, Beijing and Tianjin also have the highest shadow prices of water, at respectively 912.21 and 831.86 CNY per m3, compared to a range of 79.31 to 263.03 CNY per m3 in cities in Hebei. Virtual water flows from cities in Hebei to Beijing and Tianjin thus generate economic gains. It is estimated that virtual water trades in the JingJinJi region have generated a net economic gain of 403.62 billion CNY in 2012, particularly owing to trades of agricultural products from Shijiazhuang to Beijing and Tianjin. [ABSTRACT FROM AUTHOR]

Electricity demand in megacities may exert substantial stress on water resources, which is often expressed through the water scarcity footprint for electricity consumption (WSFE). Conversely, water scarcity may constrain electricity production, leading to increased vulnerability for megacities electricity production. The WSFE and the water related vulnerability of electricity production reflect two aspects of water-electricity conflict. This varies over time by both the amount and location of electricity production. However, no studies have conducted time-series analysis to evaluate the trends of these two indicators, both in terms of severity and spatial characteristics. Our study focused on evaluating trends in water-electricity conflict both within and beyond megacity administrative boundaries. China's four provincial-level megacities, i.e. Beijing, Tianjin, Shanghai and Chongqing, were chosen as case studies. The results show that water related vulnerability of electricity production in Tianjin, Beijing, Shanghai and Chongqing was diverse and can be classified as extreme, severe, moderate and minor, respectively. Between 2006 and 2016, the WSFE of Tianjin experienced an increasing trend, and its water related vulnerability of electricity production remained at the highest level. Beijing's WSFE has decreased, but its water related vulnerability of electricity production has increased. These differing trends highlight the need for joint reductions to both WSFE and water related vulnerability of electricity production in mitigating water-electricity conflict. [Display omitted] • Water related vulnerability of electricity production was dynamic during 2006–2016. • Water related vulnerability in four Chinese megacities was diverse. • Tianjin had the highest water related vulnerability and water scarcity footprint. • The external water scarcity footprint of Beijing was the largest, but decreasing. • Changes in water related vulnerability may differ to water scarcity footprint. [ABSTRACT FROM AUTHOR]

• Megacity water resource network should include physical and virtual water supply. • Input-output analysis is used to analyze megacity water vulnerability. • Megacities were more vulnerable to external than internal water scarcity. • Virtual water inflow help decrease vulnerability in water stressed megacities. The water resource networks that provide water for urban consumption consists not only of physical water supply, but also water embodied in imported goods and services i.e. virtual water supply or external water footprint. However, it remains unknown that if relying on external water footprint will increase or decrease the vulnerability of cities' water resource networks. Here, we evaluate the vulnerability of urban water resource networks for China's six megacities i.e. Beijing, Tianjin, Shanghai, Chongqing, Guangzhou, and Shenzhen. The vulnerability index was developed through combining a refined multi-region input-output table with both water footprint and water scarcity footprint analysis. The results showed that megacities need to import large volumes of virtual water embodied in food related sectors to balance their physical water shortages. The external blue water footprint (BWF) of the six megacities accounted for 80.7% of their total BWF, and was almost twice their physical water supply. The large share of external BWF helped Beijing, Tianjin, and Shanghai, which suffer extreme water stress in their urban areas, to decrease their total vulnerability by 39%, 33%, and 28% respectively, but conversely increase their vulnerability to external water shortages i.e. indirect vulnerability. Establishing megacity physical and virtual water resource networks based on input-output analysis provides an opportunity for urban water planners to internalize the risk of their external water footprint. Avoiding import water-intensive products from regions suffering extreme water stress, or managing indirect vulnerability through cooperation with those regions are suggested as viable water management approaches. [ABSTRACT FROM AUTHOR]

• The water scarcity footprint enables meaningful spatial comparisons of water impact. • We compared the water scarcity footprint of energy demand for 6 Chinese megacities. • Our results highlight the impacts of energy demand extend beyond the city boundary. • The water scarcity footprint of northern Chinese megacities is higher than southern. • Fossil fuel processing in northern China contributes to scarce water consumption. Water is required throughout the life-cycle processes of energy production to meet the growing energy demands in China's megacities. However, the spatially explicit impact on water scarcity both inside and outside the megacity boundaries from megacities' energy demands remains unknown. We quantified and compared the water footprint and water scarcity footprint for final energy demand (WFE and WSFE) in China's megacities from a consumption perspective. Six acknowledged megacities, i.e. Beijing, Tianjin, Shanghai, Chongqing, Shenzhen and Guangzhou, were evaluated with an extended multi-region input–output model. The results showed that these megacities were endowed with only 2.60% of the national available water resources, but their WFE (WSFE) made up nearly 14.00% (13.50%) of the national total. The megacities located in Northern China generated a larger WSFE in their WFE than the cities in Southern China. Energy demands in these megacities were heavily dependent on scarce water sourced from beyond their administrative boundaries, together importing 84.10% of WSFE from elsewhere. Electricity demand dominated the volumetric water consumption, representing 52.00% of the WFE. The distribution was different for scarce water consumption, with coal demand generating 34.00% of total WSFE, followed by electricity (31.00%) and petroleum (26.00%). Although Northern China is faced with dire water scarcity, its scarce water is still being predominantly outsourced to support energy demands in both Northern and Southern megacities, mainly due to their coal and petroleum reserves. Location-specific pathways and foci should be applied for different megacities to decouple their energy demands and their scarce water consumption. [ABSTRACT FROM AUTHOR]